Special color-developing resin agents for no-carbon copying paper and methods for preparing such agent were studied in two process routes. The first route gave emphasis on using the single structure of zinc salicylates. Though this kind of resin has advantages of fast developing at a low temperature and developing good bright colors, the defects are that color-developing strength is light and light-aging resistance is poor, and the like. Representative examples include Japanese Laid-open Application No. 11-129614 discloses ingredients of a color-developing agent and pressure-sensitive copying materials prepared by using the color-developing agent. Japanese Laid-open Application No. 10-217607 discloses ingredients of a color-developing agent and pressure-sensitive copying materials prepared by using the color-developing agent. Japanese Laid-open Application No. 2001-261628 discloses a preparation method of multivalent metal salts of salicylic acid derivatives. Japanese Laid-open Application No. 2001-261629 discloses a method for preparing salicylic acid derivatives. Japanese Laid-open Application No. 2001-169424 discloses a method for preparing salicylic acid derivatives. Japanese Laid-open Application No. 2000-109448 discloses a method for preparing salicylic acid derivatives. Japanese Laid-open Application No. 2000-239224 discloses a method for preparing salicylic acid derivatives. Japanese Laid-open Application No. 2000-168231 discloses a method for preparing a color-developing emulsion used for pressure-sensitive paper. Japanese Laid-open Application No. 6-135132 discloses a method for preparing a color-developing emulsion used for pressure sensitive paper. Japanese Laid-open Application No. 6-293699 discloses a method for preparing salicylic acid derivatives and the use of metal salts thereof in color-developing agent. Japanese Laid-open Application No. 8-53536 discloses a method for preparing multivalent metal salts of salicylic acid resin and the use thereof. Japanese Laid-open Application No. 6-227117 discloses a method for preparing salicylic acid derivatives and the use of metal salts thereof in color-developing agent and the like.
Additionally, Chinese Patent Application Nos. 1031235A, 87107802A, 88102163A, 1229032A, 1247130A, 1276299A and 1040377A provide a single structure of zinc salicylate resins.
Another route emphasizes the single structure of phenolic resins. Though advantages of this kind of resin are that color-developing strength is heavy and light-aging resistance of writing is good, prominent disadvantages are that colors are not bright, its coating yellows easily when it is exposed to the air, and developing speed at a low temperature is slow. Representative patents include U.S. Pat. Nos. 54,020,185 and 5,017,546. The product is obtained by using an alkyl substituted phenol, formaldehyde and a metal compound as feedstocks to carry out the condensation reaction.
Chinese Patent Application No. 1200378A discloses a novel color-developing agent resin composition that is a blend of graft copolymers of a multivalent metal salt of an organic carboxylic acid and a phenolic resin. That application overcomes defects of the two kind of color-developing resin agents aforesaid. However, the composition still has disadvantages that developing speed at a low temperature is slow, colors are not bright, and the emulsion is difficult to stabilize.